Gas hydrates in deep ocean sediments. Final report 1 April 1981-30 October 1983

The purpose of this research was to elucidate the composition, state, and origin of gas in marine sediments, with particular emphasis on gas hydrates. Gas hydrates are ice-like chlathrate structures in which gases are occluded within a crystalline lattice under appropriate conditions of high pressure and low temperature. Gas and core samples from Deep Sea Drilling Project/International Phase of Ocean Drilling (DSDP/IPOD) Site 533 on the Blake Outer Ridge in the Northwest Atlantic and Sites 565-570 in the Middle America Trench of the Pacific were obtained for molecular and isotopic analyses. On Leg 76 gas samples were collected from the first successful deployment of a pressure core barrel (PCB) in a hydrate region. The sampling confirmed the presence of gas hydrates. Geochemical evidence for gas hydrates in sediments of the Blake Outer Ridge includes (1) high concentrations of methane, (2) a sediment sample with thin, mat-like layers of white crystals that released a volume of gas twenty times greater than its volume of pore fluid, (3) a molecular distribution of hydrocarbon gases that excluded hydrocarbons larger than isobutane, (4) results from pressure-core barrel experiments, and (5) pore fluid chemistry. The gas was biogenic. In contrast to the finely dispersed hydratesmore » in the Atlantic bottom sediments, gas hydrates were recovered at three sites during Leg 84 in Pacific sediments with massive hydrates being recovered in a 3 meter section at Site 570. Again, hydrate methane appeared to be biogenic.« less